The present invention generally involves nozzle assemblies for rock-drilling bits and more particularly discloses a nozzle assembly having a backflow valve combined with a replaceable nozzle insert. Presently, conventional rock bit structures utilize fluid ejection nozzles which are set into the main body of the drilling bit and communicate with fluid passages inside the bit. Generally, these nozzle assemblies are placed in tandem with backflow valves above the nozzle openings. Present structures utilize nozzles which are integrally formed in the bodies of the nozzles and have a single size opening therethrough. Replacement of the nozzles to change diameter of the openings or to replace eroded nozzles requires replacement of the entire nozzle body. Likewise, the replacement of the backflow valves which may be located above the nozzle bodies inside the nozzle cavity usually requires removal of the nozzle body.
As an example, the Nickles patent U.S. Pat. No. 3,198,269 illustrates the drill bit having a centrally-located backflow prevention valve placed between the lugs of a rolling-cutter drill bit. Removal of this valve assembly requires disassembly of the rock bit from the drill string and removal up through the central bore of the bit or removal of the rolling cutters to remove the valve through the bottom of the bit. Likewise the Talbert patent U.S. Pat. No. 3,401,758 discloses a rock drilling bit having a centrally located flow control valve which must be removed upward through the bit. The Talbert patent also discloses separate jet nozzles in the bottom portion of the bit body, independent from the flow control valve.
The patent to Hollingshead U.S. Pat. No. 3,685,601, discloses a rock bit having a combination check-flow valve and nozzle located in the lower portion of the bit body. Replacement of eroded nozzles requires removal and replacement of the entire nozzle and check-flow valve assembly.
In copending applications Ser. No. 293,053 and 293,054, by William S. Price and Howard E. Mitchell for "FLUID PRESSURE REGULATOR FOR DRILL BIT" and "AIR PRESSURE REGULATOR FOR DRILL BIT", which copending applications are assigned to the same assignee as the present application, drill bits are disclosed which utilize nozzles requiring removal and replacement of the entire nozzle when erosion of the nozzle orifice requires replacement thereof. These two copending applications are herein incorporated by reference in their entirety. Thus, conventional nozzle construction in existing rock drilling bits requires removal of the nozzle bodies for replacement of the entire nozzles upon erosion of the nozzle orifice. The present invention overcomes these difficulties by providing a combined nozzle and backflow valve assembly which allows easy replacement of the nozzle orifice without removal of the entire assembly and without replacing the entire body.